In fluid dynamics , angle of attack ( AOA , α , or α {\displaystyle \alpha } ) is the angle between a reference line on a body (often the chord line of an airfoil ) and the vector representing the relative motion between the body and the fluid through which it is moving. Angle of attack is the angle between the body's reference line and the oncoming flow. This article focuses on the most common application, the angle of attack of a wing or airfoil moving through air.
40-423: A leading-edge extension ( LEX ) is a small extension to an aircraft wing surface, forward of the leading edge. The primary reason for adding an extension is to improve the airflow at high angles of attack and low airspeeds, to improve handling and delay the stall. A dog tooth can also improve airflow and reduce drag at higher speeds. A leading-edge slat is an aerodynamic surface running spanwise just ahead of
80-639: A dogfight or during takeoff and landing, the LERX generates a high-speed vortex that attaches to the top of the wing. The vortex action maintains the attachment of the airflow to the upper-wing surface well past the normal stall point at which the airflow separates from the wing surface, thus sustaining lift at very high angles. LERX were first used on the Northrop F-5 "Freedom Fighter" which flew in 1959, and have since become commonplace on many combat aircraft. The F/A-18 Hornet has especially large examples, as does
120-422: A fixed-wing aircraft and the vector representing the relative motion between the aircraft and the atmosphere. Since a wing can have twist, a chord line of the whole wing may not be definable, so an alternate reference line is simply defined. Often, the chord line of the root of the wing is chosen as the reference line. Another choice is to use a horizontal line on the fuselage as the reference line (and also as
160-591: A built-in flight computer that automatically prevents the aircraft from increasing the angle of attack any further when a maximum angle of attack is reached, regardless of pilot input. This is called the 'angle of attack limiter' or 'alpha limiter'. Modern airliners that have fly-by-wire technology avoid the critical angle of attack by means of software in the computer systems that govern the flight control surfaces. In takeoff and landing operations from short runways ( STOL ), such as Naval Aircraft Carrier operations and STOL backcountry flying, aircraft may be equipped with
200-430: A lower, flatter curve with a higher critical angle. The critical angle of attack is the angle of attack which produces the maximum lift coefficient. This is also called the " stall angle of attack". Below the critical angle of attack, as the angle of attack decreases, the lift coefficient decreases. Conversely, above the critical angle of attack, as the angle of attack increases, the air begins to flow less smoothly over
240-470: A maximum angle of attack is reached, regardless of pilot input. This is called the 'angle of attack limiter' or 'alpha limiter'. Modern airliners that have fly-by-wire technology avoid the critical angle of attack by means of software in the computer systems that govern the flight control surfaces. In takeoff and landing operations from short runways ( STOL ), such as Naval Aircraft Carrier operations and STOL backcountry flying, aircraft may be equipped with
280-418: A particular airspeed . The airspeed at which the aircraft stalls varies with the weight of the aircraft, the load factor , the center of gravity of the aircraft and other factors. However, the aircraft normally stalls at the same critical angle of attack, unless icing conditions prevail. The critical or stalling angle of attack is typically around 15° - 18° for many airfoils. Some aircraft are equipped with
320-454: A point along the fuselage. These are often called simply leading-edge extensions (LEX), although they are not the only kind. To avoid ambiguity, this article uses the term LERX. On a modern fighter aircraft , LERXes induce controlled airflow over the wing at high angles of attack , so delaying the stall and consequent loss of lift. In cruising flight, the effect of the LERX is minimal. However, at high angles of attack, as often encountered in
360-414: A reduction in the rate of increase of the lift coefficient. The figure shows a typical curve for a cambered straight wing. Cambered airfoils are curved such that they generate some lift at small negative angles of attack. A symmetrical wing has zero lift at 0 degrees angle of attack. The lift curve is also influenced by the wing shape, including its airfoil section and wing planform . A swept wing has
400-414: Is a fixed aerodynamic device employed on fixed-wing aircraft to introduce a sharp discontinuity in the leading edge of the wing in the same way as a dogtooth. It also typically has a slightly drooped leading edge to improve low-speed characteristics. A leading-edge root extension (LERX) is a small fillet , typically roughly triangular in shape, running forward from the leading edge of the wing root to
440-411: Is more separated and the airfoil or wing is producing its maximum lift coefficient. As the angle of attack increases further, the upper surface flow becomes more fully separated and the lift coefficient reduces further. Above this critical angle of attack, the aircraft is said to be in a stall. A fixed-wing aircraft by definition is stalled at or above the critical angle of attack rather than at or below
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#1732845156173480-456: Is only indirectly related to stall behavior. Some military aircraft are able to achieve controlled flight at very high angles of attack, but at the cost of massive induced drag . This provides the aircraft with great agility. A famous example is Pugachev's Cobra . Although the aircraft experiences high angles of attack throughout the maneuver, the aircraft is not capable of either aerodynamic directional control or maintaining level flight until
520-456: Is only indirectly related to stall behavior. Some military aircraft are able to achieve controlled flight at very high angles of attack, but at the cost of massive induced drag . This provides the aircraft with great agility. A famous example is Pugachev's Cobra . Although the aircraft experiences high angles of attack throughout the maneuver, the aircraft is not capable of either aerodynamic directional control or maintaining level flight until
560-702: The Sukhoi Su-27 and the CAC/PAC JF-17 Thunder . The Su-27 LERX help make some advanced maneuvers possible, such as the Pugachev's Cobra , the Cobra Turn and the Kulbit . A long, narrow sideways extension to the fuselage, attached in this position, is an example of a chine . Leading-edge vortex controller (LEVCON) systems are a continuation of leading-edge root extension (LERX) technology, but with actuation that allows
600-528: The thrust vectoring controller (TVC), the aircraft controllability at extreme angles of attack is further increased, which assists in stunts which require supermaneuverability such as Pugachev's Cobra . Additionally, on the Sukhoi Su-57 the LEVCON system is used for increased departure-resistance in the event of TVC failure at a post-stall attitude. It can also be used for trimming the aircraft, and optimizing
640-400: The vector representing the relative motion between the body and the fluid through which it is moving. Angle of attack is the angle between the body's reference line and the oncoming flow. This article focuses on the most common application, the angle of attack of a wing or airfoil moving through air. In aerodynamics , angle of attack specifies the angle between the chord line of the wing of
680-403: The aircraft of speed very quickly due to induced drag, and, in extreme cases, increased frontal area and parasitic drag. Not only do such maneuvers slow the aircraft down, but they cause significant structural stress at high speed. Modern flight control systems tend to limit a fighter's angle of attack to well below its maximum aerodynamic limit. In sailing , the physical principles involved are
720-403: The aircraft of speed very quickly due to induced drag, and, in extreme cases, increased frontal area and parasitic drag. Not only do such maneuvers slow the aircraft down, but they cause significant structural stress at high speed. Modern flight control systems tend to limit a fighter's angle of attack to well below its maximum aerodynamic limit. In sailing , the physical principles involved are
760-408: The airflow from the upper surface of the wing becomes more pronounced, leading to a reduction in the rate of increase of the lift coefficient. The figure shows a typical curve for a cambered straight wing. Cambered airfoils are curved such that they generate some lift at small negative angles of attack. A symmetrical wing has zero lift at 0 degrees angle of attack. The lift curve is also influenced by
800-407: The airplane. The lift coefficient of a fixed-wing aircraft varies with angle of attack. Increasing angle of attack is associated with increasing lift coefficient up to the maximum lift coefficient, after which lift coefficient decreases. As the angle of attack of a fixed-wing aircraft increases, separation of the airflow from the upper surface of the wing becomes more pronounced, leading to
840-574: The angle of attack or Lift Reserve Indicators . These indicators measure the angle of attack (AOA) or the Potential of Wing Lift (POWL, or Lift Reserve) directly and help the pilot fly close to the stalling point with greater precision. STOL operations require the aircraft to be able to operate close to the critical angle of attack during landings and at the best angle of climb during takeoffs. Angle of attack indicators are used by pilots for maximum performance during these maneuvers, since airspeed information
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#1732845156173880-522: The angle of attack or Lift Reserve Indicators . These indicators measure the angle of attack (AOA) or the Potential of Wing Lift (POWL, or Lift Reserve) directly and help the pilot fly close to the stalling point with greater precision. STOL operations require the aircraft to be able to operate close to the critical angle of attack during landings and at the best angle of climb during takeoffs. Angle of attack indicators are used by pilots for maximum performance during these maneuvers, since airspeed information
920-723: The best-known uses of the dogtooth are in the stabilizer of the F-15 Eagle and the wings of the F-4 Phantom II , F/A-18 Super Hornet , CF-105 Arrow , F-8 Crusader , and the Ilyushin Il-62 . Where the dogtooth is added as an afterthought, as for example on the Hawker Hunter and some variants of the Quest Kodiak , the dogtooth is created by adding an extension to the outer section of the leading edge. A leading edge cuff (or wing cuff)
960-412: The center of gravity of the aircraft and other factors. However, the aircraft normally stalls at the same critical angle of attack, unless icing conditions prevail. The critical or stalling angle of attack is typically around 15° - 18° for many airfoils. Some aircraft are equipped with a built-in flight computer that automatically prevents the aircraft from increasing the angle of attack any further when
1000-493: The chord line of the root of the wing is chosen as the reference line. Another choice is to use a horizontal line on the fuselage as the reference line (and also as the longitudinal axis). Some authors do not use an arbitrary chord line but use the zero lift axis where, by definition, zero angle of attack corresponds to zero coefficient of lift . Some British authors have used the term angle of incidence instead of angle of attack. However, this can lead to confusion with
1040-401: The critical angle of attack, as the angle of attack increases, the air begins to flow less smoothly over the upper surface of the airfoil and begins to separate from the upper surface. On most airfoil shapes, as the angle of attack increases, the upper surface separation point of the flow moves from the trailing edge towards the leading edge. At the critical angle of attack, upper surface flow
1080-496: The leading edge of a wing. It is usually used on a swept wing, to generate a vortex flow field to prevent separated flow from progressing outboard at high angle of attack. The effect is the same as a wing fence . It can also be used on straight wings in a drooped leading edge arrangement. Many high-performance aircraft use the dogtooth design, which induces a vortex over the wing to control boundary layer spanwise extension, increasing lift and improving resistance to stall. Some of
1120-508: The leading edge vortices to be modified without adjusting the aircraft's attitude. Otherwise they operate on the same principles as the LERX system to create lift augmenting leading edge vortices during high angle of attack flight. This system has been incorporated in the Russian Sukhoi Su-57 and Indian HAL LCA Navy . The LEVCONs actuation ability also improves its performance over the LERX system in other areas. When combined with
1160-411: The lift to drag ratio during cruise. Angle of attack In aerodynamics , angle of attack specifies the angle between the chord line of the wing of a fixed-wing aircraft and the vector representing the relative motion between the aircraft and the atmosphere. Since a wing can have twist, a chord line of the whole wing may not be definable, so an alternate reference line is simply defined. Often,
1200-436: The longitudinal axis). Some authors do not use an arbitrary chord line but use the zero lift axis where, by definition, zero angle of attack corresponds to zero coefficient of lift . Some British authors have used the term angle of incidence instead of angle of attack. However, this can lead to confusion with the term riggers' angle of incidence meaning the angle between the chord of an airfoil and some fixed datum in
1240-407: The low density of air in the upper atmosphere as well as at low speed at low altitude where the margin between level flight AoA and stall AoA is reduced. The high AoA capability of the aircraft provides a buffer for the pilot that makes stalling the airplane (which occurs when critical AoA is exceeded) more difficult. However, military aircraft usually do not obtain such high alpha in combat, as it robs
Leading-edge extension - Misplaced Pages Continue
1280-407: The low density of air in the upper atmosphere as well as at low speed at low altitude where the margin between level flight AoA and stall AoA is reduced. The high AoA capability of the aircraft provides a buffer for the pilot that makes stalling the airplane (which occurs when critical AoA is exceeded) more difficult. However, military aircraft usually do not obtain such high alpha in combat, as it robs
1320-513: The maneuver ends. The Cobra is an example of supermaneuvering as the aircraft's wings are well beyond the critical angle of attack for most of the maneuver. Additional aerodynamic surfaces known as "high-lift devices" including leading edge wing root extensions allow fighter aircraft much greater flyable 'true' alpha, up to over 45°, compared to about 20° for aircraft without these devices. This can be helpful at high altitudes where even slight maneuvering may require high angles of attack due to
1360-513: The maneuver ends. The Cobra is an example of supermaneuvering as the aircraft's wings are well beyond the critical angle of attack for most of the maneuver. Additional aerodynamic surfaces known as "high-lift devices" including leading edge wing root extensions allow fighter aircraft much greater flyable 'true' alpha, up to over 45°, compared to about 20° for aircraft without these devices. This can be helpful at high altitudes where even slight maneuvering may require high angles of attack due to
1400-399: The same as for aircraft—a sail is an airfoil. A sail's angle of attack is the angle between the sail's chord line and the direction of the relative wind. Angle of attack In fluid dynamics , angle of attack ( AOA , α , or α {\displaystyle \alpha } ) is the angle between a reference line on a body (often the chord line of an airfoil ) and
1440-437: The term riggers' angle of incidence meaning the angle between the chord of an airfoil and some fixed datum in the airplane. The lift coefficient of a fixed-wing aircraft varies with angle of attack. Increasing angle of attack is associated with increasing lift coefficient up to the maximum lift coefficient, after which lift coefficient decreases. As the angle of attack of a fixed-wing aircraft increases, separation of
1480-411: The upper surface flow becomes more fully separated and the lift coefficient reduces further. Above this critical angle of attack, the aircraft is said to be in a stall. A fixed-wing aircraft by definition is stalled at or above the critical angle of attack rather than at or below a particular airspeed . The airspeed at which the aircraft stalls varies with the weight of the aircraft, the load factor ,
1520-422: The upper surface of the airfoil and begins to separate from the upper surface. On most airfoil shapes, as the angle of attack increases, the upper surface separation point of the flow moves from the trailing edge towards the leading edge. At the critical angle of attack, upper surface flow is more separated and the airfoil or wing is producing its maximum lift coefficient. As the angle of attack increases further,
1560-410: The wing leading edge. It creates a leading edge slot between the slat and wing which directs air over the wing surface, helping to maintain smooth airflow at low speeds and high angles of attack . This delays the stall , allowing the aircraft to fly at a higher angle of attack. Slats may be made fixed, or retractable in normal flight to minimize drag . A dogtooth is a small, sharp zig-zag break in
1600-413: The wing shape, including its airfoil section and wing planform . A swept wing has a lower, flatter curve with a higher critical angle. The critical angle of attack is the angle of attack which produces the maximum lift coefficient. This is also called the " stall angle of attack". Below the critical angle of attack, as the angle of attack decreases, the lift coefficient decreases. Conversely, above
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